Magazine difference, AK 47 vs. AK 74?

I couldn't find it in any of the posts I looked at on the Saiga forums, so I asked diffen.com. They said:

"Magazines

"Magazines for both rifles are similar except for the minor changes in dimensions to accommodate different size cartridges. AK-74 magazines are polymer, and have a raised horizontal rib on each side of the rear lug to prevent their use in a 7.62x39mm AK."

So, please help me here if I'm off base. I already missed out on the group buy of 45 rounders. Does this mean my 7.62X39 magazines will hold and feed the 5.45?

And in an emergency I could shave off the horizontal ribs on each side of the AK-74 magazines to use them for the 7.62X39 round in my AK-47s?